In large scale manufacturing and assembly plants, such as those used in automobile manufacturing, hundreds of machines and their machine operators may work simultaneously. In a large production environment, the production line may include miles of conveyors. The plant itself may be millions of square feet. An increase in the precision of production timing and/or control may provide better resource allocation. Accordingly, processes and controls that keep the line moving may increase production and reduce expenses.
In a single shift, a machine station, for example at an automotive plant, may process up to hundreds, even thousands, of products. The conveyor belt may move at several feet per second. The line moves fast and operations are complex. In large assembly or manufacturing plants, thousands of machines may be grouped into more than one hundred stations. Many plants are substantially automated, where machines on the production line may be equipped with programmable logic controllers (PLCs) or industrial PCs to control machine operations, and monitor machine state.
For many different reasons, a machine may malfunction or change state and generate a fault or event code. There may be as many as one thousand fault codes associated per machine. A fault code is an industry term to indicate a symptom and sometimes the cause of a problem with a machine. Much like in a modern automobile, sensors are disposed in a machine to detect when out of the ordinary situations occur. In the case of an automobile, for example, if a door is left ajar, a fault or event code will be generated to alert the occupant that a door is ajar. Fault or event codes, when generated, may be electronically sent to a central location when a machine stops operating. Fault codes are typically stored for a short period and then discarded.
In general the machines do not generate fault codes but event codes. Most event codes do not reflect any abnormal behavior of the machine. They merely inform about the status of the machine. For example, if a machine does not receive a part in n seconds then it generates an event code to indicate that a time-out has occurred and that it may require human intervention. A fault code or event code does not necessarily mean that the machine is down. Actually many event codes are generated while the machine still runs, e.g., a machine may generate an event code saying that 10,000 cycles have passed since a tool change was done and that likely it will need a new tool soon. However such an event code may not stop operations.
In a large plant, when one machine fails, its entire station or zone may stop operating, and thus the impact of the failure may be high. Parts to be processed by the machine or station may accumulate, with machines that are feeding the halted machine becoming blocked because the buffer upstream of the halted machine has filled. Moreover, parts discharged for further processing by a downstream machine may drain from the buffer downstream of the halted machine, with machines that are drawing from that buffer becoming starved. The impact of a downed machine or station can quickly spread to other machines and stations of the production line.
The maintenance staff is best utilized carrying out its primary task of maintaining the machines with preventative maintenance. Maintenance staff's primary task also includes repairing significant equipment failures. While routine maintenance may be planned, faults are not predicted in a dynamic way. Thus, maintenance and repair resources may at times be overwhelmed in the number of fault codes received from the line. Different algorithms and analyzers have been developed using real-time sensing data from machine key parts or subsystems to estimate machine performance. Real-time processing requires many sensors embedded in machines and their signals cause a large amount of data traffic for real-time production systems (especially in the automotive industry).